1. Field of the Invention
The invention relates to integrated circuit nonvolatile memory. In particular, the invention relates to programmable resistive nonvolatile memory, such as phase change memory.
2. Description of Related Art
Nonvolatile memory stores data without requiring a continuous supply of power. Programmable resistive memory such as phase change memory is an example of nonvolatile memory. A high current reset electrical pulse melts and quenches the programmable resistive element into an amorphous state, raising the resistance of the programmable resistive element. A low current set electrical pulse crystallizes and lowers the resistance of the programmable resistive element.
Because the electrical pulse type determines the data that are stored in the programmable resistive RAM, and the characteristics of the electrical pulse depend in part on the resistance of the programmable resistive RAM cells, it is critical to manufacture the programmable resistive RAM cells with the correct resistance.
The resistance of the programmable resistive RAM cells is reduced by shrinking the size of the electrical contacts that connect the programmable resistive RAM cells to the remainder of the integrated circuit. A traditional solution to forming small electrical contacts is to rely on a photolithographic mask that defines the small electrical contacts. However, such a mask is associated with accompanying problems, such as proper alignment of the mask with the already fabricated layers of the planar integrated circuit.
Therefore, it would be desirable to manufacture small electrical contacts for programmable resistive RAM without relying on an aggressive photolithography mask to define the small electrical contacts.